Apparatus for measuring rapid cooling rates



MoToR SPEED CONTROL RELAY THERMO COUPLE FIXTURE TEMPERATURE RECORDER 26 ,Is

-I7 TIMING QUENQHING ,Is MAGNETIC CLUTCH R Wu) GN L M ME m MW 0 3A C I H M P T. N R Y E E 8 WP U E N D G A W W mN W U M C W B C D El N I R T N 6 E F DI N N W m m I m mm m ME m B L E E M m. U l R 2 T GEAR REDUCTOR w. T. HASWELL, JR

APPARATUS FOR MEASURING RAPID COOLING RATES Filed Feb. 12, 1947 Feb. 19, 1952 VARYING VOLTAGE GENERATOR POTENTIAL APPLIED TEST limits. Asta'ndard' temperature recorder oper- Patented Feb. 19, @1952 "it? UNITED ATE A ENT APPARATUS FOR MEASURING RAPlD COOLING RATES I Walter T. Haswell, Jr., United States Navy Application February 12,maipseriarno-721,982 u H soiai s. (ci.' 7; s. s59) (Granted under the act trim-eta; ls'o', is

amended April .30, 1928x3100;G;i?'15f7) :7

This invention relates to temperature recordbe used. Said voltage output is estimated for the systems, and more particularly to a system the specimens to be measured and a voltage capable oi recording very large and rapid varying inversely to the thermocouple voltage is temperature variations. applied to the recorder in series addition toithe Existing apparatus for recording temperature thermocouple voltage, which will thenrespondto variations is not ableto accurately follow rapid only the difference between the two voltage Mari.- variations overlarge temperature ranges. 'An ations a variation well within 'its capa'bilities. apparatus used in-measuring the cooling rates The recorder-temperature less the simulated upon quenching offheated metallurgical specitemperature is the temperatureofithe specimen. mens comprises afthermocouple attached to the m Referring now to the drawingin detailfiFigJ-zl specimen and electrically connected to a recordis a s'ch'e'm'atic diagrampartly in block of one .ing' device which records temperature against embodiment of this: invention lshowing the time by a stylus marking on a moving sheet of arrangement of the apparatus: which must be paper. It may be desired to measure cooling added to astandard temperature recorder. This rates of the order of 2400centigrade per second. i-5 apparatus includes a y o generator The stylus actuatingmovementqin recorders of comprising a potentiometer 3 whose resistance the type described above is incapable of the rapid windings may not be linear, a voltage source l0 movement required to fon w ch rapid t mfor energizing same and control means therefor, perature variations. However, if a varying voltand mechanical means including motor l4, clutch age is provided simulating that produced by the ago 13 and gear reductor [2 for rotating the -.contact thermocouple, and varying inversely th r t H on said potentiometer at .a controllable rate.

then the actual cooling rate can be calculated A thyratron y ing circuit 1 is also infrom the summation of these two voltages, which e ed to indicate the beginning of the qu n hwill have a variation not exceeding the limits of mg Operation t e recorder. the temperature recorder. The temperature recorder 16 may be anyavail- It'is therefore an obiectjjof this invention to able typ ti izing athermocouple '5 which supprovide a system for recording very large and plies a ig al Voltage to drive'a re rding pen 25 rapid temperature variations, across a sheetof paper 26 which is moved by the It is another object ofxthis invention to provide recorder to pp y the time base- Said p p a varying voltage-which will simulate a known M preferably marked in degrees so as to transfer temperature variati V p j the signal voltage to temperature. ,The record- It is another object of this invention'to provide s stylus 5 moves i t s t. r sp ns ve t a voltage generator whose output simulates a Voltages ppl d by the thermocouple 5 and the large temperature variation as .measure dxby' a potentiometer thermocouplg 1 r u The standard temperature recorder I6,-in com- Itis still anotherobject of this-invention to bination w the above pparatus can be used provide a voltage generator whose output simuto measure temperature Variations va y lates a large temperature variation as measured excess of that Which n measured y, th by a thermocouple and can be applied opposing recorder alone- Thisfis mp sh d by requi the variation f the thermocouple voltage to a i the recorder to m e only e diiierence temperature reqorder producing record of -the 0 between the, voltage variation from the thermodifference between the simulated temperature couple 5 and from the potentiometer instead variation and the actual variation of the large voltage variation from said thermo- Other objects aridadvantages ofthe invention couple f 1 will be apparent from the following desic ption The varymg Voltage generatoras and accompanying drawing, m Whichr prises a battery potential source l0 across which Fig 1 is a schematic diagram, partly in block, is-connected a voltage divider 9, androtaryv poof one embodiment of this invention; tentiometer 8 excited thereby. Said voltage gen- Fig 2 is a chart of curves used in connection erator is connected in series with the thermowith the embodiment in Fig. 1. W couple 5, and is adjusted, as described below, to Briefly, this invention enables existing types deliver agvoltage Variation'apprOXimat'lY equ l of temperature variation recorders such as hereb p ng h p uced by the thermocouple inbefore described to measure rates of temperalp lf 'elqu ch ng of the pa l $96 1.-

"ture change which heretofore exceeded their 3216, uQ v h fis s d ofit fvarv h ta e t be "ated 'by-thevoltag'e output of athermoco'uple may generated may 'be adjusted by "shortin livine 3 thermocouple 5, which is in series with the voltage generator, and adjusting the voltage divider 9 with the rotating tap I I set at point C on the potentiometer until the recorder reads the temperature of the specimen. The cooling time is estimated from whatever statistics may be available or by trial and error. The potentiometer 8 must then be adjusted so that as its contact arm II is rotated, its voltage output will drop to zero in the estimated cooling time. Said contact arm II is rotated by a D. C. shunt wound motor I4 through a magnetic clutch I3 and a gear reductor l2. The rotation speed may be roughly approximated by a rough adjustment of the gear reductor and accurately adjusted by the motor speed control consisting of a variable resistance I5 in series with the rotor of the motor I4. The voltage divider 9 energizes the potentiometer 8 at the points A and C. The linear resistance of the potentiometer 8 between points A and B is of a different order than that between B and C, thus providing a nonlinear output from point A and sliding contact II as contact II is rotated. When the sliding contact II reaches point A the voltage output of the potentiometer becomes zero.

In order that the voltage from potentiometer 8 can be supplied at the exact instant the specimen is quenched, a synchronizing means is provided. For this purpose a thyratron circuit 1 is quiescently operated just below its firing potential. A contact is added to the quenching fixture 6 which completes the thyratrons firing circuit the moment the specimen is immersed in said fixture. The thyratron then simultaneously energizes the magnetic clutch l3 to apply a turning torque to the potentiometer 8, and energizes the timing relay I! to apply a timing pen 2'! to said recorder paper. A stop switch 4 is included in the B+ lead to the thyratron I to enable extinction of said thyratron at the end of the run.

After setting up the potentiometer 8 as above described for the proper voltage variation, it must be zero set. This is done by manually rotating the contact II to point C and adjusting the voltage divider 9 until the recorder reads the maximum temperature of the specimen with the thermocouple 5 shorted. The contact II is then manually rotated clockwise to point A where it delivers zero voltage from the battery. This manual rotation also takes up any slack in the gear mechanism. The battery It! connections to the voltage divider 9 is made so that the voltage variation produced when contact II is rotated counterclockwise will vary in opposite direction to the variation of the thermocouple voltage when it is cooling. Contact I I is rotated counterclockwise by gear reductor I2 during the temperature run. The zero position of the recording pen should then be offset, since for this operation the pen records temperature differences, it should be set so that it can deviate in either direction without running oil the paper. As indicated in the example discussed in connection with Fig. 2, setting the particular recorder used to read 300 low was found satisfactory. A reasonably accurate calculation of the varying voltage will require the recorder to respond to temperature variations of less than 50 centigrade per second.

In Fig. 2, a sample set of curves for a temperature run are shown. The distance between the two vertical lines 22 and 23 is a measure of the cooling time. It will be noted that the timing pen 2! is generally not located at the same pointof time as the recording pen with-respectto their markings on the paper. The time lag between the pens is the physical distance between the recording pen 25 and the timing pen 21 as clearly shown in Fig. 1. In measuring the cooling time this time lag must be subtracted from the distance between the beginning of the timing curve 2| and the end of the cooling curve I9. The end of the cooling curve is easily observed from the sharp drop in the line 20 drawn by the recording pen (intersection of lines 20 and 23).

The curve I8 is a plot of the voltage output of the voltage generator of Fig. 1, plotted in degrees centigrade of simulated temperature against time in seconds, part BC of said curve is the voltage developed between points B and C of the potentiometer 8, part AB is that voltage developed between points A and B, and part AC is the zero voltage output when the sliding contact I I is between A and C of the potentiometer 8. Since these resistance values may be changed and the time of rotation of the potentiometer may also be changed, the shape of the curve l8 may be controlled between wide limits. Therefore, by plotting the estimated temperature variation it is possible to match the output curve of potentiometer 8 with reasonable accuracy.

Curve 20 of Fig. 2 is the actual temperature variation output of the temperature recorder as made by the recording pen. Curve I9 is the recorded curve 20 plus the effect of the recording pen minus the simulated temperature variation curve I8. Curve I9 is therefore the true cooling curve of the specimen under test. It will be noted that if the simulated temperature variation curve I8 is carefully estimated, the recorded variation, curve 20, is very small.

In plotting the true cooling curve IS, the offset of the recording pen must be taken into account. For an offset of 300 centigrade, points along curve I9 may be calculated from the following formula:

where at any given time, X is the ordinate of the true cooling curve I9, Y is the ordinate of the curve 20 drawn by the recorder, 300 represents the restoration of the --300 offset, and Z is the ordinate of the estimated curve I8. The length of the cooling time may be worked out from the curve, since the starting time is indicated by the timing pen, it is only necessary to read the time at which the cooling curve indicates the temperature of the quenching liquid.

Although certain specific embodiments of this invention have been herein disclosed and described, it is to be understood that they are merely illustrative of this invention and modifications may, of course, be made without departing from the spirit and scope of the invention as defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

l. A system for recording large and rapid temperature variations comprising in combination, a thermocouple, a temperature recording device responsive to the output of said thermocouple, a variable voltage generating means including a motor driven rotatable potentiometer operative to produce a varying voltage signal which is substantially complementary to the output voltage variation of said thermocoupleflin response to a particular temperature variation,

said voltage signal being introduced in series aiding with the output of said thermocouple to said recording device, whereby said temperature recording device operates responsive to the difference in voltage variation between said thermocouple and voltage generating means.

2. A system for recording the cooling rates of metallurgical specimens upon quenching, comprising a thermocouple attached to said specimen, a temperature recording device operative responsive to said thermocouple, a voltage generating means operative to generate a voltage signal which is substantially complementary to the output of said thermocouple upon the quenching of said specimen, said output of said last named means being introduced in series aiding with said thermocouple to said recording device, whereby said recording device operates to record the difference in said voltage variations, and synchronizing means associated with said voltage generator for coincidentally starting the generation of an output signal from said generator with the initiation of the quenching operation.

3. A system for recording the cooling rates of metallurgical specimens upon quenching, comprising a thermocouple attached to said specimen, a temperature recording device operative responsive to said thermocouple, a voltage generating means including a potentiometer, a mechanical means for driving same, and a power source and associated voltage divider for energizing same, said voltage generating means being operative to generate a voltage signal which is substantially complementary to theoutput of said thermocouple upon the quenching of said specimen, said output of said potentiometer being introduced in series aiding with said thermocouple to said recording device, whereby said recording device operates to record the difference in said voltage variations, and synchronizing means associated with said voltage generator for coincidentally starting the generation of an output signal from said generator with the initiation of the quenching operation.

4. A system for recording large and rapid temperature variations comprising in combination, a thermocouple, a temperature recorder responsive to the voltage output of said thermocouple, a variable voltage generating means adapted to generate a voltage varying substantially at the 5 same rate as the output voltage variation of said thermocouple in response to a particular temperature variation, the respective outputs of said generating means and said thermocouple being connected in series to the temperature recorder whereby said recording means will record only the difference in variation between said generated voltage and said thermocouple voltage.

5. A system for recording large and rapid temperature variations comprising in combination, a thermocouple, a recording means adapted to transcribe small temperature variations as measured by said thermocouple, a variable voltage generating means adapted to generate a variable voltage substantially complementary to the output voltage variation of said thermocouple in response to a particular temperature variation, means connecting said thermocouple and said voltage generating means in series aiding to said recording means whereby said recording means will record only the difierence in variation between said generated voltage and said thermocouple voltage regardless of the amplitude of the temperature variation.

6. A system for recording large and rapid temperature variations comprising in combination, a thermocouple, a temperature recording device responsive to the output of said thermocouple, a variable voltage generating means including a rotatable potentiometer operative to produce a variable voltage signal which is substantially complementary to the output voltage variation of said thermocouple in response to a particular temperature variation, synchronizing means for initiating said potentiometer produced voltage variation coincident with the temperature produced thermocouple voltage variation, said voltage generating means and said thermocouple being connected in series aiding to said recording device whereby said recording device is responsive only to the difference in voltage variation between said thermocouple and voltage generating means.

WALTER T. HASWELL, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,377,274 Porter May 10, 1921 1,753,486 Travis Apr. 8, 1930 2,114,330 Borden Apr. 19, 1938 2,197,635 Eggers Apr. 16, 1940 

